Based in Crick | South Wales & West of England
LMB Flat Roofing Specialists roof and shield logo

Extension & Dormer Flat Roofs in Crick

A seamless, clean-lined GRP or liquid roof for your extension or dormer, with a 10–20 year installation guarantee depending on system and matting. Free survey and tailored quote.

10–20 year installation guarantees, depending on system and matting

The service

What extension & dormer flat roofs involves

Extension and dormer roofs carry extra importance: they sit directly over living space, and they're often visible from upstairs windows or the garden. A leak here means damage to a kitchen, living room or bedroom, and a poor finish is on show every day.

LMB installs GRP fibreglass and liquid roofing systems on new and existing extensions and dormers. Both create a seamless, joint-free waterproof surface with neat edges and upstands.

For new builds, we work to the deck provided by your builder. For existing roofs, the covering and deck are surveyed and repaired or replaced as needed.

Who it's for

  • Homeowners building a new single-storey or wraparound extension
  • Builders needing a flat roofing specialist for an extension project
  • Owners of loft conversions with dormer roofs
  • Anyone whose existing extension roof is leaking or failing

When you need it

  • A new extension is ready for its roof covering
  • Water is coming through a ceiling under an extension or dormer
  • The dormer cheeks or roof edges show signs of water damage
  • An older felt extension roof is cracking or blistering

Why use a specialist? Flat roofs fail at details: upstands, edges, outlets and joints. LMB focuses only on GRP and liquid roofing; the survey considers these details before work is specified.

If it's ignored

What waiting really costs

A leak over an extension or dormer goes straight into living space. Kitchens, bedrooms and new interiors are expensive to repair.

Damage to new interiors

Ceilings, kitchens and flooring in new extensions are costly to replace.

Bedroom damp

Dormer leaks often show as damp and mould in bedrooms.

Wall junction failure

Poor upstand detailing lets water into the main house wall.

Visible poor finish

A messy roof is on show from every upstairs window.

Common issues to avoid

  • Leaving the roof to a general builder without flat roofing expertise
  • Poor detailing where the extension meets the house
  • Insufficient falls that leave water ponding
  • Choosing felt for a roof that's visible from the house

Our process

Five clear steps, start to finish

  1. Step 1

    Inspection

    Liam visits and inspects the covering, deck, edges, upstands, outlets and any penetrations. Free of charge.

  2. Step 2

    Diagnosis

    You get a plain-English explanation of what's wrong, what's causing it and the options: repair, overlay or replace.

  3. Step 3

    Written quote

    A tailored price for your roof with the system, scope and guarantee set out clearly. No fixed rates; any scope changes are discussed separately.

  4. Step 4

    Installation

    Preparation, deck repairs where needed, and the GRP or liquid system applied to the correct method in suitable weather.

  5. Step 5

    Check and guarantee

    Completed work checked and the applicable terms confirmed. Installation guarantees are 10–20 years, depending on the system and matting; repair terms must be agreed separately.

What you get

The benefits, in plain terms

Protects living space

A seamless roof over the rooms you use most.

Clean appearance

Crisp trims and a smooth finish that looks right from above.

Long guarantee

10–20 years for installations, depending on system and matting.

Specialist detailing

Careful upstands where the roof meets the house.

Free survey

No-cost inspection and written quote.

Insured

£5 million public liability cover.

In detail

Extension & Dormer Flat Roofs: materials, methods and options

Roofing a new extension

On a new extension, the flat roof covering goes on once the deck is in place. We'll check the deck is suitable, then install GRP or a liquid system with edge trims, upstands to the main wall and properly detailed outlets. Coordination with your builder keeps the project moving.

Dormer roofs

Dormer roofs are often small, high and awkward to access, with junctions to the main pitched roof and cheeks. Both GRP and liquid systems handle these details well. Because dormers sit over bedrooms, getting the detailing right is especially important.

Rooflights and lanterns

Many extensions include rooflights or lantern roofs. The upstands around them are a common source of leaks. GRP and liquid membranes can be dressed up and around these upstands to form a continuous, seamless seal.

Why a specialist

Why choose a GRP and liquid only roofer

Many roofers offer every type of flat roof covering: felt, rubber, asphalt and fibreglass. LMB deliberately doesn't. We work only with GRP fibreglass and approved liquid roofing systems, because both create a single, seamless waterproof surface with properly specified junctions and details.

That focus shapes every recommendation we make for extension & dormer flat roofs. We aren't trying to sell you whichever product we happen to stock. We're choosing between two modern systems on the basis of what your roof actually needs: its size, shape, deck condition, drainage, details and how it will be used.

Liam Brinkworth owns and runs the business. Contact Liam to discuss the survey, proposed work and quotation.

LMB holds £5 million public liability insurance. Liquid systems are applied as an approved installer, and installations come with a guarantee of 10 to 20 years depending on the system specified and whether it requires matting.

What affects the price of extension & dormer flat roofs? The main factors are the roof area, how easy it is to reach, the condition of the existing deck, how many details there are (pipes, vents, rooflights, upstands and outlets), whether the old covering needs stripping, and which system is specified. That is why we never quote a fixed rate. The free survey looks at each of these on your roof, so the written quote reflects the real job and the proposed scope is clear. Any changes should be discussed before additional work is agreed.

Before you call

How to check your flat roof safely

You don't need to climb onto a roof to spot most warning signs. From an upstairs window, the garden or the ground, look for cracked or blistered surfaces, moss or vegetation growing on the roof, water that stays ponded for days after rain, lifted or broken edge trims, and gaps where the roof meets a wall.

Inside, check the ceilings under the flat roof for brown stains, bubbling paint or plaster, and any damp or musty smell. Stains that grow after heavy rain are a clear sign water is getting in, even if you never see a drip.

If you can, take a few photos and note when the problem appears: after every shower, only in heavy rain, or only in wind-driven rain. That detail helps narrow down the cause before the survey and makes your free quote more accurate.

Please don't climb onto or walk on a roof to inspect it. A soft deck can give way, and wet roofs are slippery. Leave that part to us. If water is actively coming in, call us for an emergency call-out rather than waiting.

Ready to get it looked at? Request your free survey or go back to the homepage.

Questions

Extension & Dormer Flat Roofs FAQs

Can you roof my new extension?

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Yes. We install GRP and liquid systems on new extension decks across our service area.

Do you work with builders?

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Yes. We can coordinate with your builder to fit the roof covering at the right stage.

Can you fix a leaking dormer roof?

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Yes, with a targeted liquid repair or full replacement depending on its condition.

What guarantee comes with an extension roof?

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10–20 years for installations, depending on the system and matting.

How long does it take?

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It depends on size and weather. The quote will confirm the timeline.

Can you seal around rooflights?

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Yes, upstands around rooflights and lanterns are detailed as part of the seamless finish.

How much will it cost?

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We're strictly quote-only. Every roof differs in size, access, condition and detailing, so a fixed rate would not reflect the work needed on your property. The survey and written quote are free, so you'll know the exact cost before you commit to anything.

Are you insured?

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Yes. LMB holds £5 million public liability insurance.

Do you cover my area?

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We cover Bristol, Bath, Newport, Chepstow, Somerset and Gloucestershire from our base in Crick, near Chepstow. If you're nearby and unsure, call and ask.

All flat roofing services

Grey seamless flat-roof edge, gutter and brick wall in a UK residential setting. AI-generated illustration, not an LMB project.

Protect your extension.Get a free quote.

Free survey. Tailored written quote. £5m public liability insurance. Approved liquid installer. Installation guarantees of 10–20 years, depending on system and matting.

07517 190213Free Quote